The present invention relates to a construction of power transmitting device for internal combustion engines and, more particularly, to a device for transmitting, through a timing belt, the rotation of the crank shaft of an internal combustion engine to shafts which are adapted to be driven in a timed relation to the engine crank shaft, e.g. a cam shaft, fuel injection pump cam shaft and so forth.
In transmitting the rotation of crank shaft of an internal combustion engine, particularly a diesel engine, to a cam shaft and a fuel injection pump shaft, it is necessary to maintain a predetermined timed relationship between the crank shaft rotation and the rotation of the cam shaft and the like. Therefore, a timing belt is used for the power transmission between these shafts. On the other hand, the power transmission to auxiliary machineries such as cooling fan, water pump, lubricating oil pump and so forth is made through the medium of V belts.
Therefore, the crank shaft of internal combustion engine is provided with a pulley for the timing belt and also a V-pulley for driving auxiliary machineries or for taking out the engine power. To attach these pulleys to the end of the crank shaft, it is necessary to reduce the diameter of the crank shaft at the end portion thereof, and to employ a complicated attaching structure.
Due to the reduced diameter, the mechanical strength of the crank shaft is decreased at the shaft end form which the power is taken out, so that the magnitude of the power taken out through the shaft end is limited undesirably. In addition, if the diameter of the timing belt pulley is reduced for reducing the weight of the engine as a whole, the diameter of the crank shaft end has to be reduced correspondingly to further make it difficult to take out a large power.
The timing belt has a delicate structure as compared with ordinary V belts, and, therefore, is accommodated by a closed timing belt case disposed at one side of the crank case so as to be kept away from the moisture, oil and/or dusts. As the timing belt operates following the rotation of the crank shaft, the timing belt generates heat due to friction to cause a temperature rise in the timing belt case, which in turn heat up the timing belt itself, resulting in a deterioration or breakage of the latter if the belt is kept in this state for a long time.